Glossary

Cross-tier quick reference. Fuller treatment of most terms is in Chapter 0.

ALPC (Advanced Local Procedure Call). The Windows IPC primitive; in Credential Guard the agent reaches the trustlet over a single ALPC channel mediated by the Secure Kernel.

Attestation. The TPM signing a statement about the machine's measured boot state so a remote party can believe it without trusting the machine to self-report.

BYOVD (Bring Your Own Vulnerable Driver). Loading a legitimately signed but vulnerable kernel driver to obtain ring-0 execution; the residual that HVCI's unsigned-code enforcement does not close.

CAE (Continuous Access Evaluation). Cloud mechanism that re-evaluates or revokes a still-valid access token mid-session in near-real-time.

Conditional Access. Entra policy deciding whether to honor an authentication based on user, device, location, and risk.

Credential Guard. Uses VBS to hold long-lived credentials in a VTL1 trustlet (LsaIso.exe) so a compromised VTL0 cannot read them.

DPAPI (Data Protection API). Windows' standard per-user secret encryption at rest, keyed off the user's credentials.

EKU (Extended Key Usage). An OID in an Authenticode signature constraining what the signed binary may do; trustlets require two specific Microsoft EKUs.

Entra ID. Microsoft's cloud identity provider (formerly Azure AD).

HVCI (Hypervisor-Enforced Code Integrity). Uses the hypervisor to guarantee kernel code pages are signed and immutable and writable pages non-executable.

Hypervisor. The layer beneath the NT kernel that creates the VTLs; the bottom of the on-box TCB once VBS is on.

Kerberoasting. Requesting a service ticket for any SPN and cracking its encrypted portion offline to recover a weak service-account password (ATT&CK T1558.003).

KDC (Key Distribution Center). The domain controller service that issues Kerberos TGTs and service tickets.

LSASS (lsass.exe). The Local Security Authority Subsystem; performs authentication and historically held the secrets it used.

Measured boot. Recording each boot stage into the TPM's PCRs (remembering), as distinct from Secure Boot (preventing).

NTOWF / NTLM hash. The MD4 of the user's password; password-equivalent, hence Pass-the-Hash.

Pass-the-Hash / Pass-the-Ticket / Pass-the-PRT. Authenticating by replaying a stolen credential artifact (the NT hash, a Kerberos ticket, or a cloud Primary Refresh Token) without the password.

PCR (Platform Configuration Register). A TPM register you can only extend (hash-chain), forming a tamper-evident summary of the boot.

Pluton. A Microsoft security processor integrated on the CPU die and updatable through Windows Update.

PPL (Protected Process Light). NT-kernel process protection (e.g. RunAsPPL for LSASS); complementary to, not a substitute for, Credential Guard.

PRT (Primary Refresh Token). The cloud analog of the long-term credential, issued to a joined device and (on capable hardware) bound to a TPM key.

RBCD (Resource-Based Constrained Delegation). A Kerberos delegation feature abusable to mint service tickets as any user when an attacker can write the target computer object's delegation attribute.

Root of trust. The one component whose trustworthiness is assumed because nothing beneath it can verify it; on Windows, in silicon.

Secure Boot. Firmware refusing to run improperly signed bootloaders/firmware.

Secure Kernel. The small kernel running in VTL1; hosts the trustlets.

Sealing. Encrypting a secret under a TPM policy so it unseals only when the PCRs match a specified state (e.g. BitLocker).

SLAT (Second-Level Address Translation). The CPU feature the hypervisor uses to make VTL1 memory unmappable from VTL0.

SSP (Security Support Provider). A pluggable authentication-protocol module in LSASS (NTLM, Kerberos, cloudap, Schannel).

TCB (Trusted Computing Base). The set of components that must be correct for a security guarantee to hold; the chain works to shrink it.

TGT (Ticket-Granting Ticket). The Kerberos credential, obtained from the KDC, exchanged for per-service tickets.

TPM (Trusted Platform Module). A tamper-resistant chip/enclave holding keys, performing fixed crypto, and measuring the boot.

Trustlet. A Microsoft-signed user-mode process running in VTL1 (e.g. LsaIso.exe); LsaIso is Trustlet ID 1.

VBS (Virtualization-Based Security). Using the hypervisor to create the isolated VTL1 secure world.

VTL0 / VTL1. Virtual Trust Levels: the normal world (kernel, drivers, your code) and the secure world the hypervisor isolates from it.

VSM master key. A VTL1-only key, TPM-sealed under PCR policy, that wraps any persistent trustlet state.